Our long-term objective is to determine how astrocytes contribute to optic neuropathy in primary open angle glaucoma (POAG). Our laboratory and others have provided evidence that astrocytes are the cells responsible for many pathological changes in the glaucomatous optic nerve head (ONH). Our Specific Aims are: 1) To identify variations in expression of genes in ONH astrocytes of African Americans (AAs) compared with age-matched Caucasian Americans (CAs). 2) To identify mechanisms, which regulate the transition of quiescent astrocytes to reactive astrocytes and mechanisms that regulate specific functions associated with the reactive phenotype. 3) To identify specific genes which are expressed by reactive astrocytes in response to different stimuli. 4) To identify the mechanisms that maintains the reactive astrocyte in the glaucomatous ONH. 5) To characterize the molecular interactions between astrocytes and axons that may lead to a non-supportive microenvironment that damages remaining axons and underlies the progression of optic neuropathy. We will use oligonucleotide microarrays and computational analyses to determine whether AAs have a distinctive gene expression profile in ONH astrocytes compared to CAs. Quantitative RT-PCR, in situ hybridization, immunohistochemistry, and biochemical assays will confirm microarray data. We will use specific inhibitors and activity assays to identify the signaling pathways and determine the regulation of functions associated with the reactive astrocyte. Using oligonucleotide microarrays and computational analyses, we will determine whether exposure of astrocytes to elevated hydrostatic pressure, a proinflammatory stimulus, or to an oxidative stress induce differential gene expressions that are specific to each type of stress. By comparing expression profiles between reactive astrocytes exposed to elevated hydrostatic pressure and glaucomatous astrocytes grown in culture, we will identify gene expressions responsible for maintenance of the reactive phenotype. Using co-cultures of normal and glaucomatous ONH astrocytes and a neuronal cell line, we will determine whether gene products expressed by ONH astrocytes under hydrostatic pressure or in glaucoma affect positively or negatively neuronal survival in vitro. This research is significant because we seek to identify novel gene expression or regulatory pathways that contribute to the susceptibility of AAs to glaucomatous optic neuropathy. By determining how quiescent astrocytes become reactive astrocytes and how the reactive phenotype is maintained in the ONH, we may discover therapeutic targets to encourage specific reactive astrocyte responses that are supportive of axonal survival or to suppress those that are destructive. Our studies to characterize the molecular interactions of astrocytes and axons that may produce a non-supportive microenvironment for remaining healthy axons in the glaucomatous ONH will demonstrate mechanisms underlying progression of glaucomatous optic neuropathy.